As flowmeters, various types are known. Many of them are configured to be incorporated in midway a pipe passageway (see Patent Document 1). These known flowmeters suffer the problem that the flowmeter when incorporated acts as a passageway resistance, thus resulting in significant pressure loss of the transported fluid. Another problem thereof is the need to stop the fluid transport in order to incorporate the flowmeter in an existing pipe passageway. They suffer a still further problem of inability to be readily moved to a site where a flow rate determination is needed.
Further, some flowmeters are capable of effecting flow rate determination from the outside of the pipe passageway, as is the case with e.g. a supersonic wave flowmeter utilizing the ultrasonic propagation period or the Doppler effect (see Patent Document 2). With this too, an apparatus or the like needs to be mounted to a pipe passageway, so there is the problem of its mounting requiring significant trouble. In particular, if the site to be determined is located at a hardly accessible location such as a high site, the mounting operation requires great trouble and mounting cost.